I only like frozen if they've been blended extremely well or if they were made in one of those slush machines. For most homemade margaritas, I vote on the rocks.
“Life is not orderly. No matter how we try to make it so, right in the middle of it lose a leg, fall in love, drop a jar of applesauce.” - Natalie Goldberg
Frozen is tough for a party. You're better off making a big pitcher and people can just serve themselves. I prefer on the rocks anyway.
Set up a station with an ice bucket, a plate with lime juice and bowl with salt, extra limes for garnish, and the pitcher of margarita. People can serve themselves and use salt or not.